1. Field of the Invention
Pedal driven bicycles continue to be used as a mode of transportation. And, this is true more today than ever before because of the diminishing supply of petroleum which has been the dominant source of energy for power driven vehicles. Bicycles and other pedal operated vehicles usually are chain driven from a driving sprocket operated by foot pedals to a usually smaller wheel driven sprocket. For many years the driving ratios between the sprockets were fixed. There then followed development of means in the wheel associated sprocket to change the driving ratios to the driven wheel. As a rule this change speed mechanism was contained within the wheel hub and required lever means shifted by the driver to effect changes in wheel driving ratios. In such an arrangement the number of driving ratios was obviously limited because of the small size of the hub.
More recently the market has seen the advent of bicycles in which the different ratios were obtained at the position of the pedal driving sprocket and at the rear driven sprocket. Various means have been employed in this position and including multiple sprockets which require the shifting of the chain from one sprocket to another when ratios are to be changed. More speed ratios are obtainable at this position but the shifting of the chain from sprocket to sprocket is not too stable and the actuating means for the driver is somewhat complex. In all of the cycles on the market with multi-speed transmissions the operator is required to manually shift some lever mechanism to accomplish speed changes.
The present invention is directed to an automatically operable speed change transmission for bicycles or other chain driven vehicles or devices without the operator thereof doing any shifting of levers or the like.
2. Description of the Prior Art
A preliminary patent search was conducted and numerous patents were found which had similar characteristics, but no prior patent disclosed an automatically operable transmission comparable to that of applicant. The diameter of applicant's driving sprocket is effectively and automatically changed by external factors resisting the pedalling of that bicycle. For many years others have attempted to and some actually did change sprocket diameters to gain different bicycle speeds. The following patents among many others were considered before the making of this present application for patent.
______________________________________ Leggo, Jr. 522,427 Leggo, Jr. 524,830 Van Eyck 593,285 Hayot 2,584,447 Bell et al 2,827,797 Hunt 3,798,989 Clark 3,800,613 Hagen 3,850,045 Bravin 3,861,232 Hunt 3,861,227 Gregory et al 3,867,851 ______________________________________
Leggo, Jr. U.S. Pat. No. 522,427 is a two speed device which employs a plurality of hinged arms with a single sprocket tooth at each outer end thereof. In one position of the hinged arms the outwardly projecting tooth at each arm's end forms with the other arms a relatively small diametered sprocket whereas when the arms are swung about their hinges so the other ends are projecting outwardly the teeth at those other ends form a relatively large diametered sprocket. It is by this means of swinging arms to either of two limiting positions that two speeds of a bicycle are obtained.
Leggo, Jr. U.S. Pat. No. 524,830 employs radially moving sprocket tooth segments. In this device slotted levers H are arranged to actuate the cam disc E to effect a radial movement of the sprocket teeth. The main feature of this Leggo, Jr. device is to retract the sprocket teeth when its effective diameter is being changed.
Van Eyck U.S. Pat. No. 593,285 employs spring urged sprocket tooth segments which are manually adjusted to different radial positions.
Hayot U.S. Pat. No. 2,584,447 shows a plurality of small sprockets mounted on the outer ends of independent spring arms to supposedly comprise one changing diameter driving sprocket. However, as the spring arms are independent of each other the resultant sprocket will take a peculiar shape. Where the chain exerts a great inward pressure or force on an arm it will swing that one arm inwardly to a great degree. However, the chain does not exert equal forces on the several arms carrying sprockets and hence the sprocket teeth are irregularly positioned -- not in any manner forming a circular sprocket. This irregular shape is especially evident where the chain has no engagement with the arm carrying sprockets.
Bell et al U.S. Pat. No. 2,827,797 describes the changing of a driving sprocket shape for a bicycle from elliptical to round. This is ostensibly to accomplish an easier pedalling for portions of the circumference of the driving sprocket when it is in an elliptical shape. However, it would seem that in other portions of the elliptically shaped sprocket it would require added resistance to pedalling.
Hunt U.S. Pat. No. 3,798,989 employs manually shiftable sprocket sections to effect driving ratio changes in a bicycle drive.
Clark U.S. Pat. No. 3,800,613 shows a manually adjustable sprocket by means of a plurality of hinged arms, each of which carries a sprocket at its outer end. The adjustment is effected by the use of inclined ramps to move the sprockets inwardly or outwardly to change the driving ratio.
Hagen U.S. Pat. No. 3,850,045 employs a plurality of radially adjustable sprockets. Curvilinear paths are provided between two plates and it is in these paths that each sprocket is journaled. When one or the other of the plates is braked the sprockets move inwardly or outwardly in the spiral like paths to accomplish a change in the driving ratio.
Bravin U.S. Pat. No. 3,861,232 shows a construction in which toothed segments of a sprocket may be adjustably positioned on a disc blank so that sprockets of various diameters may be made.
Hunt U.S. Pat. No. 3,861,227 shows a manually adjustable, variable diameter bicycle transmission sprocket.
Gregory et al U.S. Pat. No. 3,867,851 is a variable diameter sprocket which has toothed segments which are movable in a spiral path somewhat similar to the previously discussed Hagen U.S. Pat. No. 3,850,045. Again, the diameter of this patented device is changed by braking the segment holding disc causing the segments to move up or down the spiral track.